[kybernetikos]

My understanding is that most studies suggest that working around the 60 hours per week mark results in diminished productivity compared to 40 hours per week after only about 3 weeks.

On the other hand, I think people who say that they are only able to get through 4 hours of work in a day, really specifically mean programming. And it's probably true in that limited sense, but all the other stuff - communicating with others so you know what program to write, helping others so they can work more effectively, is actually very valuable. It's just a common programmer failing to not really see that stuff as 'real work'. It's even worse as programmers get promotions and are expected to spend a significant amount of their time on management type activities.